Inkjet printing mechanisms use cartridges, often called "pens," which shoot drops of liquid colorant, referred to generally herein as "ink," onto a page. Each pen has a printhead formed with very small nozzles through which the ink drops are fired. To print an image, the printhead is propelled back and forth across the page, shooting drops of ink in a desired pattern as it moves. The particular ink ejection mechanism within the printhead may take on a variety of different forms known to those skilled in the art, such as those using piezo-electric or thermal printhead technology. For instance, two earlier thermal ink ejection mechanisms are shown in U.S. Pat. Nos. 5,278,584 and 4,683,481, In a thermal system, a barrier layer containing ink channels and vaporization chambers is located between a nozzle orifice plate and a substrate layer. This substrate layer typically contains linear arrays of heater elements, such as resistors, which are energized to heat ink within the vaporization chambers. Upon heating, an ink droplet is ejected from a nozzle associated with the energized resistor. By selectively energizing the resistors as the printhead moves across the page, the ink is expelled in a pattern on the print media to form a desired image (e.g., picture, chart or text).
To clean and protect the printhead, typically a "service station" mechanism is supported by the printer chassis so the printhead can be moved over the station for maintenance. For storage, or during non-printing periods, the service stations usually include a capping system which substantially seals the printhead nozzles from contaminants and drying. Some caps are also designed to facilitate priming, such as by being connected to a pumping unit that draws a vacuum on the printhead. During operation, clogs in the printhead are periodically cleared by firing a number of drops of ink through each of the nozzles in a process known as "spitting," with the waste ink being collected in a "spittoon" reservoir portion of the service station. After spitting, uncapping, or occasionally during printing, most service stations have an elastomeric wiper that wipes the printhead surface to remove ink residue, as well as any paper dust or other debris that has collected on the printhead. The wiping action is usually achieved by either moving the printhead across the wiper, or moving the wiper across the printhead.
To improve the clarity and contrast of the printed image, recent research has focused on improving the ink itself To provide quicker, more waterfast printing with darker blacks and more vivid colors, pigment based inks have been developed. These pigment based inks have a higher solid content than the earlier dye based inks, which results in a higher optical density for the new inks. Both types of ink dry quickly, which allows inkjet printing mechanisms to use plain paper. Unfortunately, the combination of small nozzles and quick drying ink leaves the printheads susceptible to clogging, not only from dried ink and minute dust particles or paper fibers, but also from the solids within the new inks themselves. Partially or completely blocked nozzles can lead to either missing or misdirected drops on the print media, either of which degrades the print quality. Thus, keeping the nozzle face plate clean becomes even more important when using pigment based inks, because they tend to accumulate more debris than the earlier dye based inks.
Indeed, keeping the nozzle face plate clean for cartridges using pigment based inks has proven quite challenging. With the earlier dye-based inks, periodically wiping the printhead with an elastomeric wiper was sufficient. However, with the advent of the pigment-based inks, a secondary operation of cleaning the wiper has become necessary to remove sticky pigment ink residue from the wiper. In the early printers using these pigment based inks, this secondary wiper cleaning operation was accomplished using a rigid plastic scrapper bar. Through relative motion of either the scrapper, the wiper blade, or both, the wiper was scrapped across the rigid scraper bar to remove ink from the surfaces of the wiper blade. For instance, one earlier wiper scraper system used in the DeskJet.RTM. 850C, 855C, 820C and 870C models of inkjet printers, produced by the Hewlett-Packard Company of Palo Alto, Calif., required intricate ink wicking channels to draw the liquid portions of the ink away from the main scrapper surface and into an absorbent ink blotter member.
Unfortunately, the pigment-based ink residue often accumulated on the wiper surface in the form of a paste, which the earlier plastic scrapper was not totally effective in removing. Instead, when encountering this paste-like consistency of ink residue, the plastic scrapper tended to smear the ink on the surface of the wiper, rather than removing the residue. Another disadvantage of the plastic scrapper is believed to be wear on the wiper, with the scrapper actually removing fine microlayers or otherwise pitting and damaging the wiper surface. Another drawback of the plastic scrapper is the tendency of the wiper blade when moving past the scrapper to flick ink off of the cleaning surface. This ink splatter or flicking action propelled the ink residue to other areas and components inside the printer service station, dirtying any surfaces where it landed. Additionally, the plastic scrapper system typically provided only two cleaning surfaces for the wiper, assuming that the wiper moved reciprocally back and forth across the scrapper. Finally, one of the major annoyances of the rigid wiper scrapers was the aggravating noise generated by the wiper scraping process.
Thus, a need exists for an inkjet printhead wiping system including a wiper cleaner capable of accommodating both fast drying dye-based and pigment-based inks, which is quiet, insensitive to paste-like ink build-up on the wiper, which minimizes wiper wear and ink flicking from the wiper blade, and which provides an expanded cleaning surface for the wiper.